Synthesis of new late transition metal P,P-, P,N-, and P,O- complexes using phosphonium dimers as convenient ligand precursors.

ABSTRACT

The phosphonium dimer [-Cy2PCH(OH)CH2-]2(X)2, X = Cl(-), Br(-) was used to synthesize and characterize a variety of late transition metal complexes containing chelating phosphino-enolate (PCy2CH═CHO(-)), imine (PCy2CH2CH═NR, R = Ph, (S)-CHMePh), and oxime (PCy2CH2CH═NOH) ligands. The phosphonium dimer, when deprotected with base, generates the phosphine aldehyde PCy2CH2CHO in situ, which, in the presence of [M(COD)Cl]2, M = Rh, Ir, and a PF6(-) salt, or [Ni(H2O)6][BF4]2, facilitates a condensation reaction with an amine or hydroxylamine to form phosphino-imine or phosphino-oxime metal complexes [M(COD)(P-N)][PF6] or [Ni(P-N)2][X]2, X = ClO4(-), BF4(-), respectively. In the absence of an amine, phosphino-enolate containing complexes are formed. A neutral Ni(II) complex Ni(PCy2CH═CHO)2 with trans-bis(phosphino-enolate) ligands which resemble ligands used on nickel for olefin oligomerization, as well as neutral Rh(I) and Ir(I) 1,5-cyclooctadiene complexes M(COD)(PCy2CH═CHO) are characterized. Both the rhodium and iridium complexes are active olefin hydrogenation catalysts. Reaction of the phosphino-aldehyde with Pt(COD)Cl2 results in the formation of trans-PtCl2(PCy2CH2CHO)2 with pendant aldehyde groups, and under certain conditions, they undergo an intraligand aldol condensation to form a disphosphine ligand.